We have had a problem with our furnace and air conditioner for about 3 years now. The problem worsens when it is super cold or super hot outside, but the problem remains pretty constant. We have a gas furnace...and in the winter time the furnace will kick on and blow warm air, and then anywhere from 2 minutes to 20 minutes later, it loses heat and starts blowing cold air. The only way to resolve the issue is to turn the heat off for a minute, then turn it back on. So we know it's getting heat--it's just not keeping it. In the summer, it's the same thing. The air will kick on, and then anywhere from 2 minutes to 20 minutes later, it's blowing warm air instead of cold. So its the exact same problem with the heat and the air, which leads me to believe there could be a wiring problem. My husband was insistent that it was the thermostat--THREE times, so we've replaced it 3x. He finally realizes this winter, that it has to be something else. I'm thinking wiring issue--which I know nothing about this stuff...he's thinking that it could be the relay or the circuit board or something. All I know is I'm miserable!! He's a mechanic and very handy--so he could probably fix most of the things that it would be--anyone have any ideas? The furnace and ac unit are about 15 years old.

One thing I didn't mention before, is that this never happened until we changed out the thermostat for the first time. We went from one of those old round ones--to a digital one...I would think if it was something wrong with that though--it would never work--rather than it sometimes does.....

For anyone reading this with the same problem....the heating side of the problem was the flame sensor. It was dirty and needed cleaning. They just charged me the service call for that, so it was an easy $85 fix. We'll see about the air conditioning side when it gets to summer---he's thinking maybe air duct leaks....